Abstract

Most insect societies can be classified as either primitively or highly eusocial. Primitively eusocial insect societies are usually led by queens who are morphologically indistinguishable from the workers and use aggression to control the workers, thereby typically holding top positions in the colony’s dominance hierarchy. Highly eusocial species have morphologically large queens who regulate worker reproduction through pheromones, and achieve larger colony sizes than their primitively eusocial counterparts. Ropalidia marginata is a primitively eusocial wasp, but queens in this species do not usually lead the colony's dominance hierarchy and use pheromones to signal their presence to workers. Since new colonies are founded by one or a few individuals and grow through time, young colonies are small enough to permit suppression of worker reproduction through aggression. Queens in small colonies indeed sometimes occupy the top position in the colony's dominance hierarchy. It is thus possible that queens in R. marginata switch from physical control to chemical regulation of worker reproduction within the life cycle of a colony. Alternately, queens might use pheromones to maintain their reproductive monopoly, irrespective of colony sizes, the queen's position in the dominance hierarchy being an artefact of colony size. We analysed data from 100 colonies of R. marginata to test these two competing hypotheses, and found support for the latter. Our findings are consistent with the hypothesis that the evolution of highly eusocial societies from primitively eusocial ones involved a one-step transition from physical control to chemical regulation of worker reproduction.